1. Field of the Invention
The invention relates in general to a touch control system, and more particularly to a capacitive touch control system.
2. Description of the Related Art
Accompanied with ever-progressing technologies, operating interfaces of recent electronic products have become increasingly user-friendly and intuitive. For example, through a touch screen, a user can directly interact with applications as well as input messages/texts/patterns with fingers or a stylus, thus eliminating complications associated with other input devices such as a keyboard or buttons. Existing capacitive touch sensing technologies can be roughly categorized into resistive, capacitive, electromagnetic sensing, ultrasonic and optical types.
A capacitive touch control panel includes multiple electrodes, whose capacitance values are changed due to a user touch. By detecting and measuring the changes in the capacitance of the electrodes, a position of a touch point can be determined. Taking the mutual capacitive touch control technology for example, transparent electrodes forming a matrix pattern are disposed at the back of a sensing panel, as shown in FIG. 1. In this example, the electrodes parallel to the x-direction are driving electrodes, and the electrodes parallel to the y-direction are receiving electrodes. Each of the driving electrodes is connected to a driver 12, and each of the receiving electrodes is connected to a receiver 14. The drivers 12 sequentially send out driving signals, and the receivers 14 sequentially receive sensing signals. When a touch event takes place, capacitance coupling is caused between the driving electrode and the receiving electrode corresponding to the touch point, giving rise to a change in the sensing signal associated with the mutual capacitance. According to the position of the receiver 14 that detects the change in the sensing signal and the position of the driver 12 that sends out the driving signal at the time of the touch event, a subsequent circuit may determine the x-coordinate and y-coordinate of the touch point.
The driving signals sent by the drivers 12 are generally square wave signals. As known to a person having ordinary skill in the art, an ideal square wave signal is consisted of sinusoidal waves of different frequencies. As slopes of rising edges and falling edges of a square wave signal get steeper, a part constituted by a high-frequency component in the square wave signal gets larger. For a mobile communication device (e.g., a smart phone) adopting a touch control screen, the high-frequency component in the driving signals pose interference on neighboring communication circuits, even leading to performance degradation of those circuits. As shown in FIG. 1, a distribution range of the driving electrodes is directly proportional to the size of the sensing panel. That is to say, all circuits near the sensing panel are exposed to potential interference from the driving signals, which resultantly create a quite large influence range.